1. Field of the Invention
The present invention relates to lighting devices that efficiently combine a plurality of light sources and that combine lights from different types of light sources, thereby allowing an image quality to be improved. Further, the present invention relates to projection type image display apparatuses using the lighting devices.
2. Description of the Background Art
In recent years, LEDs have been used as light sources for generic illumination, since they have long service life and high light-emission efficacy. The use of LEDs as light sources for projection type image display apparatuses is under consideration, since, for example, LEDs have long service life, do not include mercury, and do not rupture. However, LEDs have a broad light-emitting surface area and poor light-converging efficiency, and therefore, as light sources for projection type image display apparatuses in which light must be converged on an image display element that is a small-scale unit, at present, LEDs have not been used for projection type image display apparatuses other than ultra-compact apparatuses which cause no problems even when output of light is low.
Therefore, methods for increasing output of light, such as by using and combining a plurality of LED light sources, or combining LED light sources and another light sources, have been proposed. For example, as shown in FIG. 13, in Japanese Laid-Open Patent Publication No. 2006-39338, a large number of LEDs 1311 are arranged and optically combined, thereby improving light output.
Further, as shown in FIG. 14, in Japanese Laid-Open Patent Publication No. 2009-259583, a fluorescent material 1411 that allows green light to pass therethrough and that wavelength-converts blue light into green light, is disposed on an optical path for a green LED. As an excitation source for the fluorescent material, a laser beam is used. Since a laser element allows light to be converged on a small surface area even when output is increased, a point light source having high output can be formed. As a result, green light brightness is increased, and improvement of light output of an output image is achieved.
Here, etendue is used as a definition of light which allows for optical handling. When it is assumed that there are no limitations on optical parts in a projection type image display apparatus, among light emitted from a light source, light for the same etendue as the etendue of a liquid crystal panel or DMD used as an image display element, can be handled. The etendue is defined as follows:etendue=π×A×(sin θ)2  (1),wherein                A denotes the surface area of a portion at which light is handled, and        θ denotes a converging angle relative to the portion A, or a light-emitting angle.        